FEDERALCOMMUNICATIONSCOMMISSION

CONSUMER INFORMATION BUREAU

INTERFERENCE HANDBOOK

.

This electronic version of our "Interference to Home Electronic Entertainment
Equipment Handbook" is provided as a service to our customers on the World Wide
Web by the Compliance and Information Bureau of the FCC.

Interference is any unwanted signal which precludes reception of the best
possible signal from the source that you want to receive. Interference may
prevent reception altogether, may cause only a temporary loss of the desired
signal, or may affect the quality of the sound or picture produced by your
equipment.

Interference to home electronic equipment is a frustrating problem; but,
fortunately, there are several ways to deal with it. This handbook provides a
step-by-step process for eliminating the interference.

If your problem is not eliminated by following the steps in this handbook,
you should follow the instructions in the owner's manual of your equipment for
contacting the manufacturer. We have provided a list of
manufacturers. If the manufacturer of your equipment is not listed, look at
the beginning of the list for additional help.

Table of Contents

I. Check the Installation of Your Equipment

Many interference problems are the direct result of poor equipment
installation. Cost-cutting manufacturing techniques, such as insufficient
shielding or inadequate filtering, may also cause your equipment to react to a
nearby radio transmitter. This is not the fault of the transmitter and little
can be done to the transmitter to correct the problem. If a correction cannot be
made at the transmitter, actions must be taken to stop your equipment from
reacting to the transmitter. These methods may be as easy as adjusting your
equipment or replacing a broken wire. These and other simple corrections may be
accomplished without the help of a service technician.

A. Simplify the problem

Begin by disconnecting all equipment from the piece of equipment you are
trying to fix. For example, if you are working with a television set, disconnect
your VCR, stereo speaker wires and video game. Then, reconnect each of these
additional devices individually to determine which device may be causing the
interference to your television. Do the same thing for a telephone or stereo
system. Disconnect all answering machines, telephones, CD players, facsimile
machines, modems, etc. If the problem goes away when a device is not connected
you have found the problem. It may be necessary to filter the device reacting to
the transmitter.

B. Check your connections.

Make sure all cables are properly fastened and in good condition. Antenna
wires, interconnecting cables and power cords often act as antennas and carry
the interference into your system. All wires and cables should be as short as
possible. If there are any loose connections or broken and damaged cables have
them replaced or repaired. If you are using cable television services and have
an in-house wire repair contract, contact your cable company for repair or
replacement of the wires.

You should also test all splitters used in your system, if there are any. (A
splitter is a device that provides a signal to more than one location.) To test
the splitter, bypass it by hooking the antenna/cable connector directly to one
TV. If the signal quality is improved or the interference goes away, the
splitter is defective and should be replaced.

C. Check your amplifier.

Temporarily disconnect the amplifier and bypass it. By doing this, you allow
the signal from the antenna to go directly to the TV or radio receiver. If the
interference disappears, then the amplifier is causing the problem.

If your TV or radio receiver is connected to a master antenna television
system (MATV), commonly used in large apartment complexes, you should contact
the building management for assistance.

D. Check your antenna system.

Even though your antenna does not have moving parts, the wire and the antenna
physically deteriorate due to the effects of time and harsh weather. Replace
damaged or broken antennas. If the antenna is badly corroded clean or replace
it. Check the incoming wire from your antenna for physical damage. If you are
using twin- lead cable, replace it with coaxial cable. If you are currently
using an inside antenna, try to replace it with an outside antenna to improve
the signal.

Twin lead is usually a flat wire that connects the antenna to a receiving
device. It is not shielded and the entire length of wire acts as an antenna.
This may cause some receiving problems such as ghosting. Coaxial cable consists
of two concentric conductors (an inner conductor and an outer braided sleeve)
and is used in cable tv installations to prevent unwanted leakage from the cable
system as well as entry of unwanted signals into the cable system.

If after following the steps described above your system continues to react
to the interference, you should continue reading this booklet.

II. Identifying Other Sources

A. Simplify the Problem

As a general rule, the more complex a system is, the more difficult it is to
isolate a problem. Always start with the simplest system possible; one
telephone, one television receiver, or just the stereo receiver.

For example, if your television is reacting to a nearby radio transmitter,
remove all accessories, such as video games, VCRs, stereo system connections,
booster amplifiers and even cable boxes. If you are connected to a cable system,
connect the cable input directly to your TV set.

If the reaction stops when you disconnect any device, you have found the
problem. You must now make a decision. You can attempt remedial action, contact
the manufacturer for assistance, or replace the device with one that does not
react to the nearby transmitter. If you choose remedial action continue with
this section.

B. Collect Information about the Interference

Some basic information about the interference will help a lot in identifying
its source.

1. When do you get the interference?

Keep track of the time of day you usually receive the interference. Do you
get interference only at dinnertime? Does the interference occur day after day
at the same time? Does the interference occur at all times or is it
unpredictable?

If your equipment is reacting to the transmissions of a nearby radio
operator, you will have the interference only when the radio operator is
talking. The pattern will be much like that of a normal conversation except that
you will hear only one half of the conversation. Usually the interference will
occur for brief periods during specific times of the day.

If the interference is on constantly, it is not caused by a nearby radio
operator. You may have electrical, broadcast, or paging interference.

2. What does the interference sound like?

Listen carefully to the interference. Read this section and see which part
best describes the interference you are experiencing.

Do you hear music and voices from a broadcast station in the background? If
so, try to identify which station you hear.

Stereo and other newer televisions may have separate audio channel
capabilities. A foreign language that synchronizes with the video, a description
of what is happening on the screen, or even continuous traffic reports may
indicate that your television is switched to the separate audio channel. Refer
to your operator's manual for instructions on how to change the audio channel.

Do you hear radio operator voices? Are the voices garbled? If the
interference is intermittent and you hear clear or garbled voices, you are
probably picking up the transmissions of a nearby CB or Amateur radio operator.
If so, you will probably be able to see an antenna mounted on their house or
car.

Do you hear static, or a constant buzzing sound like bacon frying? You may be
picking up interference from an electrical device in either your house or your
neighbor's house. You may also be picking up interference from electrical power
lines. If the buzzing noise only occurs for short periods of time, you may be
receiving interference from a household appliance, such as a hair dryer, vacuum
cleaner, or electric drill.

Do you hear voices and tones? If so, you may be picking up a nearby paging
system. Paging systems usually operate 24 hours a day, so your equipment may
react to paging interference at any time.

3. What does the interference look like?

a. Electrical Interference

Electrical interference many times will be seen as two or three horizontal
lines on the television screen and may be accompanied by a loud buzzing or
sizzling sound through the TV speakers or stereo system. Many times the lines
move upwards on the television screen and may be on for hours at a time or for a
few seconds at a time. In severe cases, the entire screen may be covered with
rolling horizontal lines.

A simple way to discover if the source of interference is in your home, is by
going to the main fuse or circuit breaker box in your home. Using your TV set or
a portable AM radio, determine whether the interference is active. Electrical
interference will sound about the same on an AM radio as it does on your TV so
you can use a portable AM radio as a detector. Assuming the interference is
occurring, you should follow these steps to identify the circuit in your house
that has the device causing the interference. Be very careful to avoid contact
within anything in the box except the fuses or circuit breakers. Remove one fuse
at a time, or shut off one circuit breaker at a time. If the interference stays
on, turn the circuit breaker back on and try the next. If you are using your
television to know that the interference is active, when you turn off the power
to the circuit that supplies power to your TV to test that circuit, plug the TV
into another circuit.

If the interference stops when a fuse is removed or a circuit breaker is
turned off, go to the area that receives the electricity supplied by the
disconnected circuit. Turn the power back on and wait until the interference is
present. Next unplug each device on the circuit one at a time. If the
interference stops after you unplug a device, you have found the culprit. The
device causing the interference must be repaired or replaced. Remember that the
device might be hidden. For example, you may have a bad amplifier in your attic,
or a defective doorbell transformer that is connected directly to the power
circuit.

An alternative method to locating electrical interference is to tune to a
quiet frequency at the lower end of the AM dial. If you hear static or a buzzing
sound, check to see if it corresponds with the interference to your TV or
telephone. If it does, use the portable radio as a detection device to locate
the source of the interference.

The noise will be loudest in the room where the interference is originating.
Unplug each electrical device in the room one by one until the interference
stops.

If you cannot locate the interference source in your own house, check with
your neighbors to see if they also receive interference. The house that has the
worst interference will most likely be the source of the interference. If your
neighbor has strong interference, you may wish to try to track it down with a
portable AM radio or run the circuit breaker test described above.

If you determine that the interference is not caused by any device in your
home or that of your neighbors, contact the customer service department of your
local power company.

b. Interference to Television (TVI)

The
following pages illustrate what many common types of interference look like on a
TV set. Find the one that best matches your interference.

Use this picture for comparison with the other pictures in this section.

TV stations
are intended to serve viewers only within a limited distance of their
transmitters. You can improve picture quality by raising your antenna or using a
more directional antenna. Check your antenna line and connections. Try
reorienting your antenna for better reception. If necessary, consider installing
an outdoor antenna or a booster amplifier. Changing from flat twin lead to
round, coaxial cable may also help.

Double images
of a TV program, or "ghosting", is a common problem with off-air TV reception in
urban areas. Ghosting may be caused by the TV signal being reflected off of a
tall building or mountains. Ghosting may also indicate problems with the TV
antenna or lead in wire. Reorient your antenna, or install a shielded (coaxial)
lead in wire. You may need to install a directional, outdoor antenna.

Images from
two different programs may appear on your TV screen when your set simultaneously
receives two TV signals. Co-channel interference looks much like ghosting,
except that the two images are different, as though one picture has been placed
on top of the other. If the problem is caused by atmospheric conditions, it is
usually temporary. Installing a directional, outdoor antenna, or relocating your
indoor antenna may improve reception. You may also have similar interference if
you are picking up signals leaking from a cable TV system. If you believe that
you are picking up cable TV stations but you are not connected to the cable
system, contact the cable TV company.

This picture
may appear on your TV screen when your set is reacting to signals from a CB,
amateur, police, or other two-way radio transmitter. The pattern will appear
only when the operator transmits. The "lines" in the interference pattern may be
wider, or may seem to "roll" up through the TV picture. If your TV is reacting
to CB or amateur radio transmissions, you will often hear the operator's voice,
although it may be garbled. If you are very close to the transmitting antenna,
the TV screen may "black out" when the operator transmits. It is also very
common to pick up the CB or amateur operator's voice on the telephone or on your
radio or stereo system. For information about possible remedies see Section III.

This picture
may appear on your TV screen when your set is reacting to an electrical device
operating in or near your home. Home appliances and electrical equipment, such
as hair dryers, electric razors and electric drills may cause temporary
problems. You may choose to live with this type of interference as it is often
expensive to correct. You may also experience intermittent problems from other
home appliances, such as refrigerators and air-conditioners. For example, you
may notice interference on your TV when your air conditioner cycles on or off.
If the interference is on continuously, it may be caused by power line
equipment. For information about possible remedies, see Section III.

Doorbell transformers are a common source of interference to TV reception.
This interference looks like snow or bars on the TV screen. It looks very much
like electrical interference, except it does not cover the whole screen. It
appears as bars of electrical interference. A frying or sizzling sound comes and
goes at about seven second intervals (the intervals may vary). The interference
may also be received hundreds of feet from the source. If you suspect that you
are experiencing interference from your own or your neighbor's doorbell
transformer, and are unable to locate the transformer, you may wish to contact a
service technician.

This pattern
may appear on your TV screen if you are picking up signals from an FM broadcast
transmitter. For information about possible remedies, see Section III.

This type of picture may appear on your TV screen if you operate a computer
in close proximity to the TV antenna. The interference may look like electrical
interference or a series of diagonal dashed white lines among other patterns.
Computer interference will usually occur only when the computer is very close to
the TV antenna. You may try to reorient your antenna or computer cables, or move
the computer or TV set to another location. For information about possible
remedies, see Section III.

Low power
radio devices, such as garage door openers also can cause interference. This
pattern may appear on your screen, if you are picking up signals from a garage
door opener or radio frequency doorbell.

Booster amplifiers are often used to help receive weak or distant TV signals.
Booster amplifiers may be installed at the TV set, at the TV antenna, or even in
the attic. Although booster amplifiers do increase the TV station signal
strength, they may also cause interference to your TV or even your neighbor's
TV. A variety of patterns may appear on your TV screen because of booster
amplifier interference. Sometimes a wavy pattern may appear, or the screen may
black out for a short time. If your antenna system uses a booster amplifier, you
should disconnect it and turn it off. Next connect your antenna directly to the
TV. If the interference disappears, have your booster amplifier repaired or
replaced. If you still have interference after disconnecting your booster
amplifier, you may be receiving interference from a neighbor's amplifier. If
several of your neighbors have interference, the one with the most severe
interference is probably the one with the defective amplifier.

Amplifiers may also generate interference when used near strong signal
sources, such as TV and radio broadcast stations, paging transmitters, or two-
way radio stations.

c. Summary of Possible Interference Sources

1) Broadcast

AM Radio Station

FM Radio Station

TV Station

2) Two-way Radio Transmitters

Citizens Band (CB)

Amateur (Ham)

Taxi

Police

Business

Airport/Aircraft

3) Paging Transmitters

4) Cable TV

5) Electrical Devices

Doorbell transformers

Toaster Ovens

Electric Blankets

Ultrasonic pest controls (bug zappers)

Fans

Refrigerators

Heating pads

Light dimmers

Touch controlled lamps

Fluorescent lights

Aquarium or waterbed heaters

Furnace controls

Computers and video games

Neon signs

Power company electrical equipment

Alarm systems

Electric fences

Loose fuses

Sewing machines

Hair dryers

Electric toys

Calculators

Cash registers

Lightning arresters

Electric drills, saws, grinders, and other power tools

Air conditioners

TV/radio booster amplifiers

TV sets

Automobile ignition noise

Sun lamps

Smoke detectors

III. Remedies

WARNING - - TO AVOID ELECTRICAL SHOCK, ELECTRIC OR ELECTRONIC EQUIPMENT
SHOULD BE MODIFIED ONLY BY QUALIFIED SERVICE TECHNICIANS

Before you attempt any of the following solutions, you should see if moving
or reorienting the affected device eliminates the interference. This often will
prove to be a simple, but effective solution. For example, you may notice that
your living room TV has perfect reception, while the bedroom TV has horrible
interference. The farther away the affected device is from the interference
source, the less severe the reaction will be.

If you believe that you are picking up interference through connecting cables
or the antenna lead, you may wish to wrap several turns of the cable through a
snap- together ferrite core.

It is always best if the affected device is modified in your home while it is
reacting to the interference. This will enable the service technician to
determine where the interfering signal is entering the equipment.

A. OFF-AIR or CABLE TV RECEPTION PROBLEMS

If you have reception problems such as a weak TV signal, ghosting, or
co-channel interference, see Section II.B.3.b of this booklet.

B. TWO-WAY RADIO INTERFERENCE

The steps listed below may help you to eliminate TV interference that you
experience from CB, amateur or other two-way radio stations. High-pass filters,
common-mode chokes (choke filters), snap-together ferrite cores and ac-line
filters are available from local electronics and department stores. A list of
sources of filters is also provided at the end of this book. Remember, if your
TV set or VCR has insufficient filtering or shielding, you may not be able to
correct the interference yourself. You will have to obtain help from the
manufacturer.

1. CB or Amateur Interference: Check to see if the TV volume control affects
the interference level. If it does, install a "high-pass filter" at the antenna
leads. This is a filter which will not allow signals in the the low part of the
radio spectrum to pass through it. The name "high pass filter" is all you need
to know to purchase one. If the TV volume control has no effect on the
interference level, go to step 4. If you still receive the interference after
installing a high-pass filter, go to step 3.

2. Two-way FM Interference: If you are receiving two-way FM transmissions,
such as police or taxi, you may need to install a "notch" or "band-reject"
filter at the TV antenna leads. The filter must be designed to reject the
specific transmissions that you are receiving. The electronics dealer where you
purchase the filter should be able to assist you with your selection. If you
still receive the interference after installing a notch filter, continue to the
next step.

3. Install a common-mode filter (see list) and/or common-mode choke at the TV
input. If you still receive the interference, go to the next step.

4. Disconnect the antenna lead from the TV set. If you still have the
interference with the antenna disconnected, install an ac- line filter at the
electrical outlet your TV is plugged into.

Try wrapping three or four turns of the TV set's power cord through a ferrite
core. Do this as close to the TV set as possible. You may also install a ferrite
core on the antenna coaxial cable where it enters the TV set. You local
electronics store will know what a ferrite core is and willl help you select
one.

C. FM BROADCAST INTERFERENCE

There are three common interference problems that involve FM broadcast
stations. The first problem may arise when you are receiving a distant TV signal
and a new FM station begins operating in your area. The FM signal may overpower
the weak TV signal. This problem often shows up as interference to TV channel 6
only. FM stations may also cause interference to radio receivers in your home.

The second problem is called "blanketing." It occurs when electrical or
electronic devices are very close to the transmitter and where the FM signal is
very strong. Operators of new FM stations are required to respond to all
reasonable interference complaints in the immediate vicinity of the station. If
the station is more than a year old or you live outside of the protected area,
installation of an FM broadcast band rejection filter at your TV and/or stereo
receiver antenna input leads, as well as use of a highly directional antenna may
reduce your problem. You may also wish to reposition the location of your
equipment to attempt to minimize or eliminate the problem(s).

Third, problems may occur when you are using an amplifier. Amplifiers are
devices used to increase signals from distant stations and frequently react to
strong nearby signals. If you suspect this is the case, you should install an FM
band rejection filter or a tunable FM rejection trap in the antenna line between
your antenna and booster. Some booster amplifiers have built in filters you
simply switch on or off. Consult the instruction manual of your product. In
extreme cases it may be necessary to install a second filter. Repair or replace
your booster amplifier if it is defective.

D. PAGING SYSTEM INTERFERENCE

You may hear tones or voice transmissions from a one-way paging system coming
through your TV set. The FCC requires paging system operators to assist in
resolving interference caused by their transmissions only while the paging
system is in the developmental licensing process. This is usually only within
the first year of operation. Further, the FCC requires paging companies to
resolve all interference complaints they may cause to television channels 4 and
5. If you know who the paging operator is, you may contact them directly. A
band-reject, or "notch" filter designed to reject the paging frequency may be
installed at the TV set input. If you need further assistance, you can contact
your local FCC office listed in this handbook.

E. INTERFERENCE TO VIDEO CASSETTE RECORDERS (VCRs):

Your VCR is really a television receiver without a screen. If your VCR is
receiving interference, replacing connecting wires with shielded wire (coaxial
cable) or replacing push- on connectors with screw-on connectors may solve the
problem. The solutions for interference from two-way radio, broadcasting, and
paging, described for television interference above, also apply to VCR
interference. If these do not work, contact the VCR manufacturer for alternative
solutions.

F. COMPUTER INTERFERENCE:

Computer interference will normally disrupt only your TV reception. Check all
computer connecting cables. You should especially be on the lookout for loose or
unterminated cables. Greater distances between the TV and computer may solve the
problem.

Occasionally, your computer may cause interference to your neighbor's TV
reception. If this happens, you are required to discontinue using your computer
system until you can eliminate the interference problem. Consult your owner's
manual, the computer dealer, or the manufacturer for suggestions on how to
resolve the interference.

G. TELEPHONE EQUIPMENT INTERFERENCE:

Telephone interference generally happens because telephones are not designed
to operate near radio transmitters and the telephone improperly operates as a
radio receiver.

You may contact the nearest FCC Office and request FOB Bulletin No. 10,
"Telephone Interference". You may also try the following:

1. Contact the telephone company if you are using a leased phone. The
telephone company may have responsibility for correcting interference to their
leased phones.

2. Disconnect all of your telephones and accessories such as answering
machines and take them to one telephone jack. Connect each instrument, one at a
time, and listen for the interference. If you hear the interference through only
one telephone, the interference is being generated in that unit.

3. Install a filter on the telephone line cord at the end nearest the
telephone and/or at the telephone handset cord.

Filters are very selective. (See Section IV.) They
must be designed for the type of interference your are experiencing or they will
not work. For example, if your phone is reacting to an Amateur or a CB radio
transmitter, install a filter designed for that purpose. FM broadcast
interference requires a filter designed to reject FM broadcast stations. AM
broadcast interference requires a filter designed to reject AM broadcast
stations, etc.

4. Filter the incoming telephone line with ferrite beads and snap-together
ferrite cores. You may need to experiment to find the best style of bead or core
and the best location on the cord.

5. If you cannot eliminate the interference using the above techniques, you
should consider purchasing a interference free telephone which has been
specifically designed to be immune to interference.

Cordless telephones use radio frequencies and have no FCC protection from
interference. If you are receiving nearby transmissions on a cordless phone your
only recourse is to contact the manufacturer for assistance. The remedies above
will not be of any use.

H. ELECTRICAL INTERFERENCE

If you have determined that the electrical interference is coming from within
your home or one of your neighbor's homes, you should disconnect the defective
equipment and replace it or have it repaired.

Devices such as electric razors, hair dryers, electric drills and saws can
also cause temporary interference problems. You may choose to tolerate this type
of interference since it is temporary and often expensive to eliminate. You may
wish to contact the manufacturer for assistance.

If you determine that the interference is not caused by any device in your
home, or a neighbor's home served by the same transformer, contact the service
department of your local power company. Most power companies will investigate
the problem and take steps to correct it.

I. INTERFERENCE TO OTHER EQUIPMENT

Stereos, electronic organs, and intercom devices, among others, can react to
nearby radio transmitters. When this happens, the device improperly functions as
a radio receiver. You should first determine what type of interference you are
receiving. See Section II of
this bulletin for assistance. You may try to relocate the device within your
home. It is usually impractical or expensive to modify the affected device.
Contact the manufacturer for assistance or consider changing to another brand or
model.

IV. About filters:

Most filters are very selective. A filter designed to eliminate AM broadcast
signals will have no effect upon an FM broadcast signal. Choose a filter
designed for your needs. If you have doubts contact the manufacturers listed
below to find a filter appropriate to your needs.

Notch filters are very selective. To be effective notch filters must be tuned
to the frequency of the offending transmitter. Therefore your service technician
or the manufacturer should do the installation.

V. MANUFACTURER LIST

Some manufacturer mailing addresses and contact points are listed below. It
is suggested that you provide the model number of your device, the serial
number, and any information concerning the specific problem.

For listings of consumer electronics manufacturers not provided in this book,
you may want to contact the Electronics Industry Alliance/Consumer Electronics
Group, 2500 Wilson Boulevard, Arlington, VA 22201 (703) 907-7600.